Validating the composition of foods is a not just a matter of quality control but an issue of safety. Research is showing how nuclear magnetic resonance (NMR) spectroscopy could lead to ways to do it quickly, accurately and cheaply.
The risks of food adulteration
Food adulteration – the deliberate or accidental contamination of foodstuffs with banned substances – is an age-old problem which continues to pose modern-world dangers. In 2008, there was a poisoning epidemic in China, in which 300,000 people were made ill and six infants died due to consuming milk products or infant formula containing the industrial substance melamine. The contamination was deliberate - as melamine is a nitrogen-rich chemical, it is indistinguishable from protein on traditional tests and can therefore artificially inflate crude protein content measurements.
The incident highlights the limitations of traditional food analysis strategies. A major factor is that they rely on targeted analysis, so only certain compounds are tested for. In order to detect unexpected and unknown compounds in food and contend with the issue of 21st century food adulteration, rapid and non-specific methods of analysis are needed.
Component substitutions in the dairy industry
In the dairy industry, imitation products have begun to appear on the market to meet a demand for low-cost foods and to offer alternatives for people who do not want to consume cow’s milk. For example, there are imitation cheeses in which the milk fat and/or milk protein have been partly or completely replaced with non-milk components such as soy, starch or vegetable replacers. Meanwhile, in ice cream, vegetable oils and fats are often used as cheap substitutes for milk fat.
While these substitutions may not be directly harmful to health, they may not have the same nutritional value as the genuine items and are also more likely to contain artificial colors and flavorings. Additionally, when products are sold without labelling, such as in a restaurant, consumers may be unaware of what they are eating. Therefore, the food industry needs reliable methods to identify such items.
To date, the preferred method of analysis for cheese and ice cream has been chromatography. These techniques allow for a detailed profile to be created but, due to their lengthy sample preparation, they are labor-intensive, expensive and time-consuming.
NMR spectroscopy is beginning to reveal its potential in food analysis and has already been studied in foodstuffs including beer, juice, grapes, infant formulas and pine nuts. It has also been used to profile cheese and ice cream but, until recently, had not been put to use in the study of food adulteration.
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NMR spectroscopy identifies imitation products
A 2013 study by Monakhova et al. explored whether NMR spectroscopy could be used to identify cheese and ice creams that contain vegetable fat substitutes. They analyzed 109 cheese samples and 112 ice cream samples. They first prepared the samples by performing hydrolysis and extracting the fat, a procedure known as the Weibull-Stoldt methodology. They then carried out both 1H and 13C NMR spectroscopy.
The researchers found that, for both types of NMR, imitation cheese samples were clearly separated from the other cheeses after principal component analysis (PCA). This was also true of ice cream when analyzed with 1H NMR spectroscopy, although the greater variability in minor compound concentrations made discrimination harder than for cheese.
Additionally, by correlating NMR data with that from gas chromatography, the team were able to generate models for predicting the classification of new ice cream and cheese samples. They say that these models could be used in future for non-targeted analysis of dairy samples and, because NMR spectra contain the same information as gas chromatography, the method could allow for faster and more efficient data-gathering.
The expanding role of NMR spectroscopy
Despite its potential in the industry, NMR spectroscopy has only recently entered routine analysis in food control institutions. However, improvements in both equipment and software are increasing its accessibility.
For example, Bruker products allow for the full automation of the NMR workflow, from sample preparation and sample changing to data analysis and archive.
The Bruker Avance III NanoBay NMR device, part of the same series that Monakhova et al. used for their research, offers highly integrated state-of-the-art spectroscopy, enhancing both productivity and quality. The researchers coupled their Bruker Avance device with a Bruker Automatic Sample Changer, which lead to sample processing times of just 12 minutes for 1H NMR and 30 minutes for 13C NMR.
Meanwhile, Bruker software, such as CMC-assist can seamlessly integrate with all Bruker spectrometers for automated data analysis and Icon-NMR supports sample changers and sample preparation robots for high-throughput automated NMR spectroscopy.
- Monakhova Y, et al. Identification of imitation cheese and imitation ice cream based on vegetable fat using NMR spectroscopy and chemometrics. International Journal of Food Science 2013; 367841.
- Sharma K, Paradakar M. The melamine adulteration scandal. Food Security 2010; 2: 97-107.
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